Wave-attenuation and hydrodynamic properties of twin pontoon floating breakwater with kelp

Abstract

With the increasing awareness of environmental protection, more and more marine eco-structures are being built. Mangroves, corals and seaweeds can be combined with marine hard structures to resist marine hazards. As a kind of marine plant, kelp has the potential to weaken wave and current. In this paper, a twin pontoon floating breakwater with kelp (TPFBK) is proposed. Experimental and numerical studies are carried out in a wave flume. Firstly, comparative experimental studies of the wave-attenuation performance of TPFBK with different length kelp and the number of rows of kelp arrangements are conducted. Secondly, the mooring force of the TPFBK with different arrangements of kelp are compared exhaustively. Finally, a simplified fluid-solid coupled numerical model is developed to analyze the wave dissipation mechanism of the TPFBK with different kelp arrangements by velocity field, vorticity and turbulent kinetic energy distribution. The results indicate that the TPFBK exhibits better wave attenuation performance compared with the traditional twin pontoon floating breakwater (TPFB). At the same time, the kelp array is helpful to reduce the on-shore mooring force. However, it increases the off-shore mooring force which is very limited. The TPFBK with a single row of densely planted kelp improves wave attenuation performance mainly by reflecting wave energy, while the multi-row arrangement of kelp enhances wave energy dissipation. And the dissipation of wave energy is caused by the variations in velocity field, turbulent kinetic energy and the development and shedding of vortices.